The quality of food products and other perishables are highly dependent on storage conditions such as the temperature and the storage time from production or packing until it finally reaches the end consumer. The deterioration processes are faster when the temperature is raising due to increasing biochemical reaction rates, and therefore the quality of perishable goods declines more rapidly at high temperatures than at low temperatures.
Examples of perishable goods which need to be stored under conditions such that a particular temperature limit is not exceeded or at least not exceeded for longer than a predetermined period of time, include fresh food products, chilled food products and food products that have been pre-cooked or processed by freezing, irradiation, partial cooking, freeze drying or steaming. If such products are not stored under appropriate temperature conditions then there is a danger of propagation of microorganisms which are injurious to human health or of spoilage organisms. Further examples of products which may need to be stored under appropriate temperature conditions are certain pharmaceuticals which would otherwise deteriorate.
Currently only date marking is applied for the insurance of storage quality. By date marking only, no information is given to the consumer or others about the storage conditions to which the product has been exposed, hence the purchasers of susceptible products are not able to determine whether the product has been stored under appropriate temperature conditions during the time of storage. Relying on date marking as a sole quality criterion presupposes that the perishable product has been stored under appropriate conditions throughout the entire storage period. The end consumer will e.g. not be able to determine if a frozen product has been thawn during transportation and subsequently frozen before being put on sale. To be on the safe side, producers of perishable goods often use date marking with a wide safety margin, hence products which are actually still suitable for consumption or use are often discarded.
Therefore, there is a continuing interest in the monitoring of the time and temperature to which storage sensitive products have been exposed in e.g. food distribution chains from factory to consumer.
By supplying a perishable product with a time-temperature indicator which follows the individual product from packing to sale, the producer, the grosser, the retailer and the consumer will have a better product control than they have currently. By the use of a time-temperature indicator, the true shelf life of the products can be monitored, which means that discarding can be retarded until the applied time-temperature indicator has detected that storage conditions have not been appropriate and/or that the recommended storage time has been exceeded.
Time-temperature indicators may be classified as either partial history or full history indicators depending on their response mechanism. Partial history indicators will not respond unless a threshold temperature has been exceeded, while full history indicators respond independently of a temperature threshold and provides a cumulative response to the time and storage conditions to which the time-temperature indicator (and hence the product) has been exposed.
Thus, EP 505 449 B1 discloses an example of a partial history time-temperature indicator comprising a fusible material such as polycaprolactone triol, polyethylene glycol C1-4 alkyl ether and polyvinyl alcohol, which flows when a given threshold temperature is exceeded and re-solidifies when exposed to temperatures below the same temperature. The fusible material flows in a substrate and an indicator system produces a physically detectable change in the substrate when the fusible material flows therein.
Partial history time-temperature indicators such as the above described, do not provide a direct measure of time-temperature history. This is most important, since the degradation of perishables depend on the time exposure to particular temperatures. For example, food exposed for a period of time to one temperature may degrade to the same extent if exposed to a shorter period of time at a higher temperature. Hence there are several advantages in using full history time-temperature indicators.
However, there are a number of general requirements that a full history time-temperature indicator should fulfill. These include that the indicator gives a continuous and cumulative response to time and temperature, and that the response to time and temperature is generated gradually and is a function of both time and temperature. The response to time and temperature should be irreversible to prevent the time-temperature indicator from being reset. Preferably it should also be capable of indicating the time-temperature history within a wide temperature range.
The indicator should furthermore in conjunction with a perishable product, show the real condition of this product, and e.g. reflect the storage conditions to which the product has been exposed and be able to show if a frozen product has been defrosted for a period of time. It should also be conveniently activated so that pre-usage storage of the indicator is not a problem, and the response to time and temperature should be given in a visually and easily interpretable manner. Finally, and importantly, it should be non-toxic and not pose any thread to human health.
According to present invention there is now provided a full history time-temperature indicator which fulfill all of the above mentioned requirements. The response given by the time-temperature indicator according to the invention is easily read by the human eye, and in conjunction with a product it gives a measure of the storage conditions to which the product has been exposed by giving a cumulative response to time-temperature exposure.